Phenol-modified hydrocarbon resins are widely used in coatings and adhesive formulations, and also widely used in the manufacturing of rubber products. These resins improve the compatibility of the ingredients in such formulations. In addition, the resins provide improved chemical and weathering resistance to finished products designed to perform under harsh environmental conditions, such as wide variation of temperature, oxidation by air, and light exposure. Other advantages include the substantial improvement of the adhesive properties in coating and adhesive formulations.
Phenol-modified hydrocarbon resins encompass a wide range of products produced by the reaction between phenols and vinyl aliphatic and aromatic monomers. In general, the composition of these resins is quite complex, which can be simply characterized by a mixture of monomeric and polymeric components bearing distinct chemical functionalities. For instance, the reaction of unsubstituted phenol with vinyl hydrocarbon monomers, such as styrene, alpha-methylstyrene, vinyltoluene, indene, coumarone, or any other similar vinyl monomers, or a mixture thereof, catalyzed by strong acids, produces liquid to wax-like resins containing variable amounts of short polymers of vinyl monomers, in addition to the alkylated phenol components. The polymer fraction is mostly composed of cyclic dimers and trimers of the vinyl monomers, with small amounts of respective linear oligomers. The alkylated phenol fraction is also multicomponent, as it contains variable amounts of monosubstituted, disubstituted, and trisubsituted phenolic compounds. The compositions of these resins can be controlled by careful adjustments of the reaction conditions. However, the most significant factor to control the desired physico-chemical properties is the judicial selection of structural variations on the phenol and on the vinyl hydrocarbon monomer building blocks. Mixtures of phenols and/or vinyl monomers are very often employed to achieve the right balance of polarity, solubility, and fluidity, which is intimately related to the hydroxyl functionality, the content of aromatic, hydrophobic moieties, and polymer fractions, in addition to the molecular weight distribution. For this purpose, it is a common practice to incorporate small portions of an alkyl-substituted phenol to the reaction mixture. The most commonly used alkyl-substituted phenols are ortho- and para-tert-butylphenol, octylphenol, and nonylphenol. These phenols can be produced in-situ, prior to or after the reaction with the intended vinyl monomers. These variations in the process can add cost and complexity to the manufacturing of such resins. In addition, it can be more difficult to stabilize the process and minimize the variability between batches as the number of steps and raw materials are increased.
Cashew nutshell liquid (CNSL) contains a large concentration of cardanol and cardols, a natural source of meta-substituted alkylated phenols and resorcinols. CNSL is relatively low cost, and it is a globally available bio-renewable commodity, which makes it an ideal building block for the manufacturing of phenol-modified hydrocarbons resins. Due to the structure of the components of CNSL, the hydrocarbon resins can be manufactured with fewer steps and/or raw materials.
Among the advantages of cardanol-based hydrocarbon resins are low viscosity, improved solubility with organic solvents, very low cloud points, and compatibility with a great number of resins and polymer formulations.